This application relates to planetary gear carrier assemblies in which at least one of the components is made from a powder metal material and related methods of making such assemblies. More specifically, this application relates to improvements in the way that a ring, such as a disc lock ring, is connected to the hub of the carrier.
Planetary gear carrier assemblies are commonly used in automatic transmissions to create various gear ratios while driving a car. Such assemblies often include various gears (for example, a sun gear, planet gears, and a ring gear) that can be selectively locked together to create the different gear ratios.
In such assemblies, a disc lock ring is often coupled to the hub of the carrier in order to capture other components between the ring and an axial face of the carrier. For example, a plate for positioning the planetary disc carrier assembly relative to the rest of the transmission assembly and bearings could be captured between the carrier and the ring. In still other assemblies, clutch packs might be captured in this space between the ring and carrier.
FIGS. 1A, 1B, 2A, and 2B illustrate a prior art ring 10 and carrier 12 made from powder metal that can be connected to achieve such purposes. In FIGS. 1A and 1B, the ring 10 is generally annular in shape and has a number of radially-inward facing projections 14 or teeth with recesses 16 therebetween. Each of the projections 14 has a ridge 18 at a lower axial end of the radially-inward facing surface of the projection 14. In FIGS. 2A and 2B, the prior art carrier 12 has an axially extending hub 20 with a castellated axial end in which various projections 22 extend axially upward from the axial end of the hub 20 such that there are recesses 24 there between. The projections 22 each have sections of a circumferential groove 26 formed on a radially-inward facing surface of the projections 22.
When the ring 10 is received over the hub 20 of the carrier 12, the radially-extending projections 14 and recesses 16 of the ring 10 interlock with the recesses 24 and the axially-extending projections 22 of the carrier 12, respectively. Once the projections and recesses are nested in one another, then a circumferential channel is established by the ridges 18 on the ring 10 and the various sections of the circumferential groove 26 on the carrier 12. To axially restrict or lock the ring 10 on the carrier 12, a snap ring (not illustrated) is inserted into this circumferential channel. With the snap ring in place, the sections of a circumferential groove 26 prevent the snap ring from axial movement and the ring 10 cannot be readily removed from the carrier 12 as the ridges 18 on the ring 10 cannot pass the snap ring.
Unfortunately, through experience, it has been discovered that this prior art planetary gear carrier assembly is not as structurally robust as is desired.
As an initial concern, the flanks of the projections 22 of the carrier 12 are subject to particularly high stresses and are prone to failure or damage. When the carrier 12 is fabricated from powder metal, in order to further strengthen these castellated sections the carrier 12 may be infiltrated with copper. Such copper infiltration occurs with the carrier 12 in a position upside-down from that illustrated in FIGS. 2A and 2B (that is, with the castellated section facing downward). However, in this position, the copper still often fails to infiltrate all the way down to the castellated projections, now positioned at the bottom of the carrier 12. When copper infiltration is inconsistent or incomplete, then the castellated area remains structurally weak and the sections of the circumferential groove 26 will still be particularly prone to failure.
Hence, a need exists for a planetary gear carrier assembly made from powder metal materials in which a disc lock ring is attachable to the hub of the carrier in a manner that is less prone to failure and that can withstand higher stresses.